What is DHTML?
DHTML is a browser technology that enables elements in a document to be, well, dynamic. It is not a programming language, both rather, a set of features that is accessed through a programming language, such as JavaScript.

What can DHTML do?
While this differs greatly depending on the level of support a browser has for DHTML, DHTML in general can accomplish the following:

1) Create content that can appear and disappear AFTER the document has loaded.
2) Manipulate the style of a document (ie: font size, color etc) on demand.
3) Dynamically position elements in a document. 4) In IE 4, data binding.

How is JavaScript similar/different from DHTML?
JavaScript is similar to DHTML in that they all are web technologies whose mission is to enhance a web page. They differ, however, in one key point- JavaScript is a programming language, whereas DHTML is not. Its simply a set of features.